Building Code Impact on Smoke Control
Building codes continue to define and regulate the overall aspects of building design, construction and safety. One code type that has, in general terms, grown rather quickly from its infancy to today's more complex requirements is that of smoke control within buildings. Building codes and the standards for design and installation of smoke control systems have always gone hand in hand, each aff...
Building codes continue to define and regulate the overall aspects of building design, construction and safety. One code type that has, in general terms, grown rather quickly from its infancy to today's more complex requirements is that of smoke control within buildings. Building codes and the standards for design and installation of smoke control systems have always gone hand in hand, each affecting the other. While the principles of smoke control remain constant, code requirements, depending on the model code used, can result in a variety of applications and designs for identical building configurations and classifications.
A look at the last 15 years of code development and revision reveals the iterations and changes regarding smoke control. What was once acceptable practice has, over time and through practical experience, become outdated and replaced with more detailed requirements. As new technologies, approaches and designs continue to push the ever-evolving norms that are associated with standard building practices, the codes have attempted to keep pace.
Not long ago, smoke control was at its beginnings with respect to code requirements. Going back to earlier editions of the Uniform Building Code (UBC), there were only three general instances where smoke control would be required: buildings containing atria, high-rise office or residential buildings and covered mall buildings. The requirements were in separate sections of the UBC and were not very detailed, comprising less than two pages.
Today, while the general building applications of atria, high-rises and covered malls have not changed within the UBC and its successor, the International Building Code (IBC), smoke control requirements now reside in a dedicated section of the code with multiple options to be selected and designs calculated based upon individual applications and building features. Previously accepted smoke control practices that are no longer used include the air change method and breakable or manually operated windows or panels.
In a relatively short period of time, the complete list of acceptable smoke control methods has been replaced twice over, never mind the changes to the overriding principles over smoke management. Over time and through practical experience, these practices evolved into the currently accepted methods: active pressurization, airflow or exhaust and passive containment. Specific paragraph sections within special use occupancies have grown into a dedicated section of methods.
In addition to the change in general principles over the years, the testing criteria to ensure proper operation has also become better defined. Verification for the air change method included measuring exhaust rates at a given fan or group of fans to determine whether proper airflow was being provided for the given area.
The test itself did not necessarily represent how all spaces within the area were affected, just that the fan was providing at least the designed criteria. Just because proper exhaust rates were present at fans did not mean that proper distribution of openings was provided for the area protected.
In contrast, the current IBC pressurization method test criteria is the measurement of a minimum pressure differential between the smoke zone activated and all adjacent smoke zones across all common smoke zone boundaries. Verification of the maximum pressure differential achieved is also required to ensure that occupants can safely exit without undue effort opening the door. This process ensures compliance with test criteria at every interface to adjacent areas—not just proper fan performance—and provides for safe egress of building occupants.
Smoke control—a priority?
To this day there are those who support the continued role of active, mechanical smoke control systems as one of the major tools associated with building safety. Others look at it as only a component of an overall fire-protection and life-safety scheme. Improper design, lack of routine maintenance and outside factors such as weather conditions can impact the reliability of active mechanical smoke control systems. In addition, depending on which edition of a given model code has been adopted within a jurisdiction, there can be an effect on whether a facility is even required to have a smoke control system.
Even within the model codes themselves there are differences in the types of facilities in which smoke control systems are required to reside. One such instance compares the 1997 edition of the UBC with the 2000 and 2003 editions of the IBC. While smoke control would be required for a high-rise building or any covered mall in a jurisdiction adopting the 1997 UBC requirements, it would not be required in covered malls with fewer than three levels open to one another or in a high-rise building in a jurisdiction adopting IBC requirements. To take it a step further, if neighboring jurisdictions each adopted the model language from these codes, but one chose the IBC and the other chose the UBC, high-rise buildings on opposite sides of a street separating the jurisdictions could have differing requirements for smoke control.
One could look at this as part of a building code's evolutionary process, but occurrences of multiple deaths on floors above a fire floor in partially protected facilities within high-rise buildings have been documented in several historical fires. Will the IBC further evolve to reinstate high-rise applications as requiring smoke control systems in future additions or will smoke control in high-rise buildings eventually become extinct? Reinstatement of the requirement may not be likely. However, new high-rise buildings may still incorporate active smoke control systems, driven by other factors. Opinions vary as people's priorities differ.
Smoke control has found a niche in the "performance-based" arena to assist in finding new avenues as alternates to other requirements in the current model building code. A few jurisdictions have amended their adoption of the model code to include high-rise smoke control regardless, but in most cases, use of a smoke control system as part of an overall alternate solution to offset other code requirements has been an accepted approach. For example, smoke control systems have been used to reduce the requirement for a one-hour occupancy separation or eliminate the need for a standard fire curtain or opaque curtain in stage applications. This type of system can also be used as a tool in providing alternate exit schemes for a building or when topography creates difficult access conditions for emergency responders in order to increase the amount of time occupants have to safely exit a building.
One such example can be found in Nevada where both Clark County and the city of Las Vegas amended the 1997 edition of the UBC to remove the requirement of an occupancy separation between retail and assembly occupancies, provided several provisions are met. The retail-to-assembly-occupancy separation requirements occur quite frequently in these jurisdictions where there are retail spaces located off large casino areas. Some of the provisions to the exception include the installation of a smoke control system in the retail space. While smoke control was one of many elements of the provisions, it plays a major role in the prevention of the spread of smoke from the retail space—where higher fuel loads may be expected—to the highly populated assembly occupancies, in this case casinos.
Another application where smoke control has been used as part of an alternate method to standard code requirements was in eliminating the need for a standard fire curtain protecting the opening in a stage proscenium opening. The nature of this specific production was such that elements from the show, including tracks and guides, would be traveling through the opening between the stage and the audience. This made provisions for a standard fire curtain or an opaque curtain, combined with the installation of a deluge system, impossible. As part of the design of an alternate method, an active smoke control system was provided within the stage area to restrict the movement of smoke from the stage toward the seating area.
This smoke control system was designed using the exhaust method to lift the smoke layer above the height of the opening in the proscenium wall, roughly 50 ft., to help prevent smoke from an incident on the stage from reaching the audience. Other provisions included a water curtain at the opening and a deluge system at the high bay area of the stage. All three systems—mechanical smoke control, water curtain and stage deluge—operate in conjunction with one another and activate as a result of an air-sampling system cross-zoned with flame detection located throughout the protected area. While the water systems protect the occupants from the spread of flame, the smoke control system is utilized to prevent the spread of hot gases and smoke. Together, they provide the protection intended by the fire curtain.
Current technologies and building uses continue to force the expansion of building requirements as they relate to smoke control. Whether it occurs as a result of contractors, manufacturers or building owners, the limits of current smoke control requirements continue to be identified through instances that are not contained within the code.
One such example is the requirement for elevator machine-room pressurization within high-rise buildings. Recent elevator manufacturing developments have led to elevator equipment installations that are contained as part of the elevator within the hoistway shaft. While certain current codes would require pressurization of the elevator machine room, they do not require pressurization of the elevator shaft. In this instance, is the shaft the machine room? Or will the code be revised to deal with such manufacturing developments? Building designers need to understand the intent of the code in order to apply it to the new technologies we see today.
The next level
Smoke control continues to be a tool to provide a level of protection that other systems cannot accomplish. Overall growth regarding the requirements for smoke control as part of code revisions indicates the changing requirements for buildings. The generalities associated with older codes has been replaced with specific design calculations, but the flexibility associated with the four methods of smoke control still rely on the designer to make decisions based upon building applications and conditions.
While the priorities and individual preferences associated with smoke control may vary, a properly designed and maintained system can provide protection from the spread of smoke to occupants in an emergency condition. Use in performance-based alternatives as part of an overall solution only furthers the usefulness and versatility of smoke control systems. Building codes and the requirements for smoke control will continue to evolve and grow with the construction industry. As new technologies, methods of construction and building applications arise, the evolution of smoke control through the building codes will continue to keep pace.